Differential scanning calorimetric studies on binding of N-acetyl-D-glucosamine to lysozyme

Abstract

Differential scanning calorimetric (DSC) measurements were performed on the thermal denaturation of lysozyme and lysozyme complexed with N-acetyl-D-glucosamine (GlcNAc) at pH 5.00 (acetate buffer), 4.25 and 2.25 (Gly-HCl buffer). DSC data have been analyzed to obtain denaturation temperature T_d, enthalpy of denaturation ΔH_d, heat capacity of denaturation ΔC_pd and cooperativity index Eta. From these thermodynamic parameters, the binding constant K_L and enthalpy of binding ΔH_L, for the weak binding of lysozyme with GlcNAc have been determined. The values of K^L and ΔH_L at pH 5.00 and 298 K are 42 ± 4 M^-1 and -24 ± 4 kJ mol^-1, respectively, and agree very well with the experimentally determined values from equilibrium and other studies. The binding constant has also been estimated by simulating the DSC curve with varying values of K_L (T_d) until it matches the experimental curve.